Cassegrain optical systems have been found to be particularly useful in passive optical receiver systems. Their most important advantages are decreased physical length of optical system, reflective optics, and good dynamic balance for applications such as optical seeker systems. Their main disadvantage for applications involving active (transmitting) systems is the fact that the secondary mirror occludes a large portion of the transmitted light. For well collimated sources it is virtually impossible to use standard, optically fast, Cassegrain optics as collimating objectives. Optical sources which are not well collimated and which emit light in broad beams can use Cassegrain optics but at somewhat reduced efficiency as compared to refractive objective systems.
For the above reasons, at the present time it is difficult to employ Cassegrain optics in coaxial optical transceiver systems. A technique which would render Cassegrain optics suitable for use as collimating lenses for optical sources would greatly increase the optical designing alternatives available for optical transceiver systems. A particularly useful application would be in active optical seeker heads for missiles.